Intermediate frequency transformer



Feb. 3, 1959 A. M. BOOTHE INTERMEDIATE FREQUENCY TRANSFORMER Filed Oct. 25, 1955 my i INVENTOR.

ALONZO M. BOOTHE. BY

ATTORNEYS.

2,872,649 INTERMEDIATE FREQUENCY TRANSFORMER Alonzo M. Boothe, Cincinnati, Ohio, assignor to Avco Manufacturing Corporation, Cincinnati, Ohio, a corporation of Delaware Application October 25, 1955, Serial No. 542,747 1 Claim. ('Cl. 333-77) The present invention relates generally to intermediate frequency (I. F.) signal transformers and specifically provides a miniature I. F. transformer of particularly durable construction, stable gain, and uniform band width.

A specific object of the invention is to provide a compact I. F. transformer which is suitable for the following electrical requirements:

Q of each inductance: second,

Band Width characteristics of a four-stage amplifier employing five of these transformer: 140 kilocycles (kc.) at the 6 db points and 440 kc. at the 60 db points.

A primary object of the invention is to achieve miniaturization in an I. F. transformer of the type which is particularly suitable for use in a glide slope receiver, without impairing the desired Q characteristic.

Another object of the invention is to provide, in an intermediate frequency transformer, effective means for adjusting the coupling without increasing the space requirements and after sealing of the assembly.

For a better understanding of the invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following description of the accompanying drawings.

In the drawings:

125 at 18.9 megacycles per Fig. l is a perspective view showing my improved transand showing details of a representative terminal lug and associated structure; and

Fig. is a circuit diagram of the entire transformer unit in accordance with the invention.

As indicated above, this transformer is of particular utility in a glide slope receiver.

The coupling desired in the intermediate frequency transformer in accordance with the invention is primarily magnetic, not tight, and is of a single peak critical character. In accordance with this invention this objective is accomplished within rigid space limitations by constructing the transformer in the form of two closely spaced solenoid windings with a brass shield between them to restrict the coupling, as will be described below.

The transformer circuit connections are brought out to terminal lugs 11, 12, 13, and 14, the first two of which constitute the primary terminals and the remaining two the secondary terminals of the double-tuned intermediate frequency circuit electrically illustrated in Fig. 5. The primary and secondary windings and 16 are simple closely spaced solenoids, each securely wound on a hollow externally threaded ceramic form 17 or 13. The

nited States Patent 0 to permit tuning by means fo powdered iron cores 372,649 Patented Feb. 3, 1959 forms are hollow in construction,

closed at their upper ends and open at their lower ends (secured to base 19),

slidably mounted Within the coils. Such tuning adjustments by powdered iron cores are per se well known, so that the cores are not herein shown. The coil forms are rigidly secured to a copper base member 19 and project upwardly therefrom.

Shielding is provided by a copper can 20 which is secured to the base as shown in Figs. 2 and 3. In accordance with the invention, there is provided in the can 20 a transverse conductive partition 21, made of copper or the like. The partition may be integral with the base or {can or secured to the can by a flange as indicated at '10. The partition restricts the coupling between the primary and the secondary circuits. Provision is made for adjusting the coupling in this manner: Partition 21 is slotted as shown at 22; secured to a suitable internally threaded fitting 23in the base 19 is an adjusting screw of brass or other suitable conductive non-magnetic material. Element 24 projects between the primary and secondary coils 15 and 16 to vary the coupling by adjustably closing, to a greater or lesser degree, the slot or opening 22 in the partition 21. Only a fragmentary portion of partition 21 is shown in Fig. l, and the entire partition is shown in section in Fig. 2.

The capacitance parameter in the primary circuit is supplied by fixed capacitors 25 and 26. Similarly, fixed capacitors 27 and 23 are provided in the secondary circuit.

The mechanical structural arrangement of these capacitors is unique and complementary to the coil arrangement in that the capacitors are slidably mounted on terminal posts 35, 36, 37, and 38, each rigidly secured in place near its respective corner of the base 19 by a structure such as that detailed in Fig. 4.

During assembly and after the capacitors are slipped into place on the terminal posts, a rigid assembly of capacitors and coil forms is completed in such a way that the capacitors are prevented from coming into contact with the shielding can 20. This is effected by phenolic boards 39 and 40, each apertured to receive a coil form and having eyelets such as 50 and 51 soldered to the ends of a pair of terminal posts, as shown in Fig. 1.

Coming now to the details by which the terminal posts are secured to the base and electrically brought out to their respective lugs, post 37 in Fig. 4 is representative. An enlarged metallic portion thereof, designated 41, abuts against a washer 42 which in turn is located adjacent a grommet 43. Grommet 43 is formed with an annular extended portion which projects through base 19 into a countersunk portion of a plastic insulator 44. The members 42, 43, and 44 are apertured to receive a projecting integral extension 45' of post 37, and terminal lug 14 is electrically secured to such extension.

In a practical transformer suitable for use with an operating frequency of 18.9 megacycles, the primary capacitors 25 and 26 have an a gregate value of micromicrofarads and the aggregate value of capacitors 27 and 2.8 is the same. 1

While there has been shown and described what is at present considered to be the preferred embodiment of the invention, I desire in the appended claim to secure a fair and reasonable range of equivalents.

I claim:

A double-tuned intermediate frequency transformer comprising, in combination: a rectangular copper base member; an open-mouthed copper shielding can including a transverse central copper partition having a slot formed therein, said slot opening into the mouth of the can, said can being removable from, but normally secured to, said base member with its mouth adjacent the base member; first, second; third and fourth upwardly projecting terminal posts mounted adjacent the corners of said base member; first and second solenoid coils fixedly mounted on said base member, the central axis of eachof said v coils being disposed perpendicularly to said base member, said. first solenoid coil being mounted 1 ond capacitorsand the first solenoid ina primary tuned circuit; means for interconnecting the third and fourth capacitorsandthe second solenoid-in a secondary tuned circuit, saidtuned circuits being ontopposite sides of said partition when the cani's, located on said base member;,first; and second insulating boards disposed with a gapv therebtetween, said. first insulating board being disposed. parallel to said base member and being apertured toreceive and position in rigid assembly said first and second, terminal posts, said first and second capacitors and said first solenoid coil; said second insulating board being disposed parallel to said base memberand being apertured' to receive'and position inrigidassenrbly said third and fourth terminal p0sts,;said third and fourth capacitors and said second solenoid coil; said transverse partition extending through said gap, and an adjusting screw projecting through said base member into said slot for adjusting the coupling between said primary tuned circuit and said secondary tuned circuit, the central axis of said screw being directed lengthwise of said slot; said tubular capacitors extending from said base to said in sulating boards.

' References Cited in the file of this patent UNITED STATES PATENTS Great Britain May 13, 1953 

